- Distal renal tubular acidosis
Distal renal tubular acidosis Classification and external resources OMIM 179800 MeSH D000141
Distal RTA (dRTA) is the classical form of RTA, being the first described. Distal RTA is characterized by a failure of acid secretion by the alpha intercalated cells of the cortical collecting duct of the distal nephron. This failure of acid secretion may be due to a number of causes, and it leads to an inability to acidify the urine to a pH of less than 5.3. Because renal excretion is the primary means of eliminating acid from the body, there is consequently a tendency towards acidemia. This leads to the clinical features of dRTA;.
- Normal anion gap metabolic acidosis/acidemia
- Urinary stone formation (related to alkaline urine, hypercalciuria, and low urinary citrate).
- Nephrocalcinosis (deposition of calcium in the substance of the kidney)
- Bone demineralisation (causing rickets in children and osteomalacia in adults)
The acidosis is variable, and one may have dRTA with alpha intercalated cell failure without necessarily being acidemic, this is termed incomplete dRTA. The diagnosis of dRTA can be made by the observation of a urinary pH of greater than 5.3 in the face of a systemic acidemia (usually taken to be a serum bicarbonate of 20 mmol/l or less). In the case of an incomplete dRTA, failure to acidify the urine following an oral acid loading challenge is often used as a test. The test usually performed is the short ammonium chloride test, in which ammonium chloride capsules are used as the acid load. More recently, an alternative test using furosemide and fludrocortisone has been described.
The symptoms and sequelae of dRTA are variable and ranging from being completely asymptomatic, through loin pain and hematuria from kidney stones to failure to thrive and severe rickets in childhood forms as well as possible renal failure and even death.
dRTA commonly leads to sodium loss and volume contraction, which causes a compensatory increase in blood levels of aldosterone. Aldosterone causes increased resorption of sodium and loss of potassium in the collecting duct of the kidney, so these increased aldosterone levels cause the hypokalemia which is a common symptom of dRTA.
- Autoimmune disease. Classically Sjögren's syndrome, but it is also associated with systemic lupus erythematosus, rheumatoid arthritis and even hypergammaglobulinemia. Hypokalaemia is often severe in these cases.
- Hereditary causes include mutations of Band 3 the basolateral bicarbonate transporter of the intercalated cell, which may transmit in an autosomal dominant fashion in western European cases, or in an autosomal recessive fashion in South East Asian cases. The South East Asian cases are associated with more severe hypokalemia. Other Hereditary causes include mutations of subunits of the apical proton pump vH+-ATPase, which transmit in an autosomal recessive fashion, and may be associated with sensorineural deafness.
- Liver cirrhosis.
- Nephrocalcinosis. While it is a consequence of dRTA, it can also be a cause; related to calcium-induced damage of the cortical collecting duct.
- Renal transplantation.
- Sickle cell anemia.
- Toxins, including ifosfamide, toluene, lithium carbonate and amphotericin B.
- Chronic urinary tract obstruction.
- Possible side effect of IV-administered bisphosphonates, such as zoledronate (~10%)
This is relatively straightforward. It involves correction of the acidemia with oral sodium bicarbonate or sodium citrate. This will correct the acidemia and reverse bone demineralisation. Hypokalemia and urinary stone formation and nephrocalcinosis can be treated with potassium citrate tablets which not only replace potassium but also inhibit calcium excretion and thus do not exacerbate stone disease as sodium bicarbonate or citrate may do.
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Urinary system · Pathology · Urologic disease / Uropathy (N00–N39, 580–599) AbdominalGlomerulopathy/
nephroticBy conditionType III RPG/Pauci-immuneTubulopathy/
PelvicUrethra Any/all Water-electrolyte imbalance and acid-base imbalance (E86–E87, 276) Volume status Electrolyte Acid-baseBoth
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